[bilproject]

Usually in a twin tank set up fuel is drawn from one tank and the other is connected to the tank being drawn from. as some fuel is drawn out of the tank by the engines fuel from the connected tank is siphoned over to the supply tank. Since there is a check between them the connected tank drains while the supply tank stays relatively full. There is also only one fuel gauge in the system and that is in the supply tank. See if that is not your set up.